<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
        "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
    <title></title>
    <script type="text/javascript" src="js/jquery-3.3.-1.js"></script>
    <script type="text/javascript">

           //jquery标准开发形式
          $(function (){

             $(":button:first").click(fun1);
          });

         function  fun1(){
             alert("123")
         }

    </script>
</head>
<body>
            <center>
                 <input  type="button">
             </center>
</body>
</html>